Postprandial effect of n-3 polyunsaturated fatty acids on apolipoprotein B-containing lipoproteins and vascular reactivity in type-2 diabetes.

The two primary classes of lipoproteins are apolipoprotein A and apolipoprotein B.  Both classes consist of a number of subclasses differing from each other by their apolipoprotein composition and their specific metabolic properties.  Lipoprotein subclasses have also been shown to differ in their atherogenic potential, with apolipoprotein B and C (LpB:C) being considered the most atherogenic.  Little evidence exists regarding the effect of dietary fatty acids on plasma apo B containing LPs.  The objective of the present study was two fold:  first, to investigate the effects of unsaturated fatty acids on individual apo B containing LP subclasses in the postprandial state; and second, to examine whether changes in apo B containing LP subclasses were associated with significant changes in vascular endothelial function and triglyceride (TG) status.  This study was conducted on type-2 diabetic men and women because endothelial dysfunction is common in this disease and considered a key initiating step in the development of atherosclerosis. 

Fifteen men and women (men, n=10; women, n=5) with type-2 diabetes participated in this 3 meal, randomized, double blind, crossover study.  All subjects were being treated for their diabetes with either diet or hypoglycemic agents.  All subjects completed 3 treatment sessions that were separated by ? 1 week.  At each treatment session, participants were required to consume 1 of 3 freshly prepared test meals within a 15 min period.  Test meals were provided in the form of milkshakes, and contained 473 ml of skim milk, 50g fat from 1 of 3 blends of unsaturated fatty acids, ice, and flavorings that masked flavor and aroma of the oils.  The oil blends in the test meals were as follows:  1) Control meal (MUFA):  90% safflower oil and 10% canola oil.  The MUFA diet provided 0.5g n3 fatty acids (FAs) as ALA;  2) MUFA + ALA: 70% canola oil, 20% high oleic safflower oil, and 10% safflower oil.  The MUFA + ALA diet provided 3.3g ALA; 3) MUFA + EPA/DHA:  60% high oleic safflower oil, 25% safflower oil, and 15% sardine oil to provide 2.8g EPA, 1.2g DHA, and 0.2g ALA.  Fasting blood samples were obtained at baseline, and at 2h and 4h following each test meal.  Vascular reactivity was measured via an ultrasound protocol previously described that measured flow mediated dialation (FMD) of the brachial artery before the meals and 4h postprandially. 

All dietary treatments resulted in a significant increase in postprandial levels of apo B and LpB; however, the magnitude of the change did not differ significantly between the treatment diets.  Postprandial change in LpB:C was 23% lower following the MUFA + EPA/DHA diet compared to the MUFA control.  The MUFA + ALA was found to attenuate the increase in LpA-II:B:C:D:E in subjects with high triacylglycerols (? 1.69mmol/L). Subjects with the largest increases in LpB:C exhibited the largest impairment of endothelial function. 

Although preliminary, these findings suggest that altering dietary fatty acid intake with an emphasis on ALA may have significant acute effects on specific apo-B containing LPs.  These data demonstrate that there are opportunities to target the postprandial state to further decrease risk of CVD particularly in persons with diabetes.